There is an entire sub-field of medical astrology.
http://www.greekmedicine.net/medical_astrology/Introduction.html
It has several Hellenistic bases, one of which was Aristotle's 4 qualities: hot, dry, cold, moist. Each of these relates to a temperament type (phlegmatic, choleric, sanguine, melancholic) which relates to one of the 4 Aristotelian elements (in order, water, fire, air, earth.) Water is cold and wet, fire is hot and dry, air is hot and moist, earth is cold and dry.) Each temperament type related to a bodily fluid: phlegm, blood, black bile, yellow bile.)
The idea was that imbalances in the humors were likely to cause disease. Imbalances might be prevented or corrected by diet, but sometimes more intervention was used, like the old practice of bloodletting.
Each planet possessed the same qualities of temperature and moisture: Mars is hot and dry, the moon is cool and moist, for example. Each astrological sign can be classified according to its element. (Aries is fire, Taurus is earth, and so on.)
The 6th house is the traditional house of illness. Then the human body was divided into 12 anatomical parts, corresponding to signs and houses. In the "anatomical man" Aries rules the head, Taurus rules the neck and shoulders, on down to Pisces ruling the feet.
Leo rules the spine (you're a chiropractor?)
Different planetary combinations could lead to various illnesses. For example, an afflicted planet in Aries or the first house might make the person prone to headaches or eyesight problems.
There were also special techniques for predicting length of life.
There's a lot more there, although I'm not sure how much medical astrology influenced. Aristotle.